(Update: This may have been obvious, but I confirmed with am Instagram spokesperson that when Systrom said 50 percent of users, he meant 50 percent of monthly active users — which is what I’d assumed when I suggested it was more than 75 million.)

During his presentation, Systrom also talked about the growth of general photo-sharing. He said it’s driven by three main factors — the transition to digital, the fact that we carry our cameras (i.e., our smartphones) in our pockets, and the ability to share photos on social networks. He noted that those photos run the gamut from important political moments to photos of brunch — but even a brunch pic, he said, is not just brunch, because it serves as “a visual status message” and a location check in.